The present invention relates generally to speakers for mobile communication devices, and more particularly to distributed mode speakers for mobile communication devices.
Distributed-mode loudspeakers (DMLs) are a type of loudspeaker known in the art, and were developed by New Transducers Limited (NXT®). DMLs comprise a thin but stiff speaker panel excited by a transducer. Like conventional pistonic loudspeakers, DMLs convert electrical audio signals to audible sounds that can be heard by a user. However, a fundamental difference between pistonic speakers and DMLs is in the way that DMLs generate and radiate sound energy. In DMLs, audio signals drive the transducer to excite the natural resonant modal structure of the panel. This excitation vibrates the panel in a pseudo-random manner such that different areas of the panel are independently excited with different amplitudes and phases. In other words, the DML panel actually “bends” according to the various frequencies of the vibration. These “bending waves” produce wideband acoustical output over a wide range of frequencies. DMLs eliminate the need for bulky enclosures, multiple drivers, crossovers, and other parts that are necessary in conventional pistonic speaker designs. These attributes make DMLs an attractive choice for use as a speaker in many consumer electronics devices.
Despite their advantages, DMLs have not gained widespread acceptance for use in mobile devices. One drawback is the DML's lack of robustness. DMLs require a relatively large area that makes them more susceptible to damage than other speaker designs. Speakers for mobile devices should be expected to withstand a certain amount of impact or shock when the mobile devices are dropped or hit against another object. Accordingly, there is a need for a more robust design for distributed mode speakers for use in mobile devices.